US6213273B1 - Friction liner having a network of grooves, for a clutch - Google Patents

Abstract

A torque converter includes a bridging clutch having an annular friction liner for engaging axially against a reaction surface of the clutch. The liner is in the form of an annular ring having a friction surface, an outer perimeter and an inner perimeter, with a network of grooves formed in the friction surface to enable a liquid to flow between the liner and the reaction surface. The network of grooves is not open radially in the outer perimeter of the liner.

Description

This is a divisional of application Ser. No. 08/896,214 filed Jul. 17, 1997 now U.S. Pat. No. 6,035,992.

FIELD OF THE INVENTION

This invention relates to friction liners, in particular for bridging clutches for torque converters.

More particularly, the invention relates to a friction liner of the above type which has an annular friction surface for making axial contact against a reaction surface, the liner being also of the type in which the friction surface is formed with a network of grooves to enable a liquid to flow between the liner and the reaction surface.

BACKGROUND OF THE INVENTION

Torque converters are in particular used in motor vehicles to provide a coupling between the heat engine of the vehicle and the gearbox, which may be automatic and/or of a continuously variable type. In a torque converter, the transmission of the torque is obtained by circulation of a fluid between two bladed or finned wheels or rotors, one of which is coupled to the engine and the other to the gearbox. In their construction, these two wheels are not coupled together mechanically, so that there always exists between them the possibility of relative slipping movement. In some operating modes of the vehicle, this slipping movement is of no value and can even be detrimental to the overall performance of the drive train of the vehicle.

In addition, in parallel with the torque converter, a bridging clutch is generally provided, for the purpose of making a direct mechanical coupling between the engine and the gearbox in certain operating modes, corresponding for example to quasi stabilized speed ranges. Up to the present time, such bridging clutches have been used essentially in an “all or nothing” operating mode, that is to say they are used only in a fully engaged state or a fully disengaged state.

With a view to optimizing the performance of the drive train of the vehicle considered as a whole, it is now thought desirable to use the bridging clutch in a larger number of operating modes of the drive train, and especially, for example, during gear changing operations. In addition, the bridging clutch is tending more and more to be used, no longer only in its fully engaged and fully disengaged states, but also in a mode in which it slips, in particular with a view to damping out torque variations.

Thus, there is now an increasing tendency for the bridging clutch to be operated in a way which tends to give rise to severe heating, firstly of the contact surfaces and secondly of the oil which not only controls the clutch but also cools it.

With a view to preventing this additional heating causing accelerated wear of the liners, or causing the oil to be degraded by carbonization, it has previously been proposed to arrange on the friction liners a network of grooves which give improved circulation of the oil between the friction liner and the reaction surface. Various proposals have been made as to the form of the grooves in this type of network, all of them aiming to establish communication between the outer and inner perimeters of the annular friction liner.

However, the existence of the network of grooves gives rise to a loss of oil, even when the bridging clutch is used in its fully engaged mode and when there are no longer any differences in speed between the input shaft connected to the engine and the output shaft connected to the gearbox. In addition, the presence of these grooves in the friction liner substantially reduces the effective contact surface between the friction liner and the reaction surface, to the detriment of the torque that can be transmitted without slipping by the bridging clutch.

DISCUSSION OF THE INVENTION

The object of the invention is to overcome the above mentioned problems.

According to a first embodiment of the invention, a friction liner for a bridging clutch of a torque converter, having an annular friction surface which is adapted to make axial engagement against a reaction surface, the friction liner being of the type in which the friction surface includes a network of grooves to enable a liquid to flow between the liner and the reaction surface, is characterized in that the network of grooves comprise concentric circular grooves which are connected together through radial grooves spaced apart circumferentially, in that radial grooves are open firstly into an inner circular groove and secondly at the inner edge of the liner, in that the radial grooves formed between two circular grooves are offset circumferentially with respect to the radial grooves formed between the inner circular groove and the inner edge, and in that the radial grooves are not open radially to the outside of the liner.

According to a second embodiment of the invention, a friction liner for a bridging clutch of a torque converter, having an annular friction surface which is adapted to make axial engagement against a reaction surface, the friction liner being of the type in which the friction surface includes a network of grooves to enable a liquid to flow between the liner and the reaction surface, is characterized in that the network of grooves is not open radially to the outside of the liner, and in that the liner has a spiral groove and a set of radial grooves which are open at the inner edge of the liner, the said radial grooves intersecting the spiral groove at several points.

According to a third embodiment of the invention, a friction liner, having an annular friction surface which is adapted to make axial engagement against a reaction surface, the friction liner being of the type in which the friction surface includes a network of grooves to enable a liquid to flow between the liner and the reaction surface, is characterized in that the network of grooves is not open radially to the outside of the liner, in that it has a single groove which is elliptical and centred on the axis of the liner, the major axis of the ellipse defined by the said single groove being shorter than the outer diameter of the liner, and in that radial grooves put the elliptical groove in communication with the inner edge of the liner.

The friction liner is preferably incorporated in a bridging clutch of a torque converter.

The depth of the grooves of the friction liner is preferably substantially equal to one half of the axial thickness of the liner.

The liner is preferably made of a composite material including carbon.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view showing in axial cross section a bridging clutch for a torque converter.

FIGS. 2 and 3 are enlarged cut-away views showing part of the clutch of FIG. 1, and illustrating more particularly the contact between the friction liner and the reaction surface of the clutch.

FIG. 4 is a front view of a first embodiment of an annular friction liner in accordance with the invention, for a clutch of the kind exemplified in FIGS. 1 to3.

FIG. 5 is a view in cross section taken on theline5—5 in FIG.4.

FIG. 6 is a view similar to FIG. 4 but showing a second is embodiment of the invention.

FIG. 7 is a view in cross section taken on the line7—7 in FIG.6.

FIG. 8 is a view similar to FIG. 6 but shows a third embodiment of the invention.

FIG. 9 is a view in cross section taken on theline9—9 in FIG.8.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows atorque converter10 which is arranged to be, for example, interposed between a heat engine and an automatic gearbox, in a motor vehicle.

In the known way, thetorque converter10 comprises a substantially cylindricalouter casing12 having an axis A1, which is coupled to the output shaft (not shown) of the engine of the vehicle, so as to be driven in rotation about its axis A1. Thetorque converter10 has a substantiallytransverse wall16 arranged on the side of the torque converter opposite to the engine. Thiswall16 has aninternal face14 which carries a series ofvanes18 that act as a fluid pump. Inside thecasing12, aturbine wheel20 is provided withvanes22 and is mounted for rotation about the axis A1 with respect to thecasing12. Theturbine wheel20 is arranged to drive in rotation anoutput shaft24 of thetorque converter10, which is coupled to the gearbox. Theturbine wheel20 is mounted on acentral sleeve26, which is coupled to theoutput shaft24, for example through a splined coupling.

The casing of the torque converter contains oil which provides fluid coupling between thepump vanes18 and theturbine wheel20.

Again in the known way, abridging clutch30 is arranged within thecasing12 of thetorque converter10, for coupling theoutput shaft24 of thetorque converter10 in rotation to thecasing12 when the clutch is engaged. Engagement of thebridging clutch30 thus normally prevents relative rotational slipping movement about the axis A1 between the casing12 (constituting a pump) and theturbine wheel20 that drives theshaft24.

Thebridging clutch30 includes a substantially annularmovable clutch plate32 which is mounted, through a radially-inner axialperipheral flange34, in sliding axial movement on thecentral sleeve26. Themovable clutch plate32 is also coupled in rotation to thecentral sleeve26 through an interposedtorsion damping device36, for absorbing the torque variations that occur during engagement and disengagement of the clutch.

Themovable clutch plate32 carries anannular friction liner38 at its outer periphery. Theliner38 is arranged to make axial contact against acorresponding reaction surface40 formed on the internal face of atransverse wall42 of thecasing12. Thiswall42 is the casing wall which lies axially on the same side of the torque converter as the engine of the vehicle, and may be referred to as the proximal wall of the casing, thewall16 then being the distal wall.

Theclutch liner38 may for example be made of a composite material comprising a resin in which reinforcing elements are embedded. These reinforcing elements may for example be in the form of cellulose fibers or carbon fibers. In another version, theliner38 may be of a carbon/carbon composite material.

Thus, themovable clutch plate32 defines within thetorque converter casing12 twochambers44 and46, between which theplate32 constitutes a piston, in such a way that, according to the prevailing oil pressure in each of these chambers, theclutch plate32 is urged axially in one or other direction. Thus, when thefirst chamber44, which is defined between themovable clutch plate32 and theproximal wall42 which carries thereaction surface40, is supplied with fluid under pressure, themovable clutch plate32 is pushed axially in a direction such as to cause thebridging clutch30 to be disengaged. Conversely, when thesecond chamber46 of thecasing12, defined between theclutch plate32 and thedistal wall16 and, as shown in FIG. 1, also containing the torque converter itself, is supplied with fluid under pressure, theclutch plate32 is displaced axially in a direction such as to cause theclutch30 to be engaged.

Reference is now made to FIGS. 4 to9, showing three different versions of afriction liner38 incorporating features of the invention. Theseliners38 are in the form of flat annular plate elements having an axis A1 and atransverse fastening face48, by means of which they are fastened, for example, on themovable clutch plate32, together with an opposed annular transverse face, or friction surface,50 which makes the frictional contact against thereaction surface40, FIGS. 1 to3, of thecasing12. As can be seen in FIGS. 4 to9, thefriction surface50 is formed with a network of grooves which enable oil to circulate between thefriction liner38 and thereaction surface40, especially for cooling purposes.

This network of grooves is not open radially towards the outside of theliner38. Thus, theliner38 comprises a peripheralouter ring portion52 which is solid and which has a transverse surface, constituting part of thefriction surface50, which is continuous over the whole periphery of the liner. Instead, the grooves which constitute the above mentioned network of grooves are open radially in only the innerperipheral edge62 of theannular friction liner38. These grooves can be made, in particular, either by molding or by machining.

With reference to FIGS. 2 and 3, these Figures show diagrammatically the contact between thefriction liner38 against thereaction surface40. In this connection, due to the mode of actuating of the bridgingclutch30, which is urged towards its engaged position by an excess of pressure in thechamber46 as compared with that in thechamber44, the movableclutch plate32 tends to deform, due mainly to the contact force applied between the central sleeve26 (FIG. 1) and the movableclutch plate32 in the region of itsinternal flange34.

This being so, and as is shown most particularly in FIG. 3, the movableclutch plate32 tends to deform in such a way that theliner38 makes its initial contact with thereaction surface40 through the outer peripheral edge51 (FIG. 4) of theouter ring portion52 of the liner. Subsequently, under the effect of pressure, the contact between theliner38 and thereaction surface40 spreads over the whole of thefrictional contact surface50 of the liner, as can be seen in FIG.2.

However, the use of a liner having a network of grooves which are not open radially outwardly enables the outerperipheral ring portion52 of theliner38 to form a seal once thering portion52 has made initial contact with thereaction surface40. This seal tends to prevent any loss of oil between thefriction surface50 of theliner38 and thereaction surface40, and this improves transmission of the torque.

However, if the bridgingclutch30 is controlled in such a way as to slip on thereaction surface40, that is to say if the excess pressure in thechamber46 of thecasing12 is moderated, the contact pressure between thereaction surface40 and theliner friction surface50 is reduced in such a way that a slight flow of oil will be able to pass between the twosurfaces40 and50, such as to cool them. This oil flow is assisted by the presence of the grooves which are formed in the radially inner portion of theliner38, and which limit the radial distance over which thering portion52 tends to provide sealing.

As to the form of the network of grooves in theliner38, reference is made once again to FIGS. 4 to9 which show three different versions of this network.

In the first version shown in FIGS. 4 and 5, the liner has essentially two concentriccircular grooves54 and56, which are joined together throughradial grooves58 regularly spaced apart circumferentially. In addition, furtherradial grooves60, again spaced apart at regular intervals, are open firstly into the innercircular groove54 and secondly in theinner edge62 of theliner38. In this embodiment, theradial grooves58 formed between the twocircular grooves54 and56 are offset circumferentially with respect to the otherradial grooves60 which extend between the innercircular groove54 and theinner edge62.

In the second embodiment which is shown in FIGS. 6 and 7, theliner38 has asingle spiral groove64 and a set ofradial grooves66 which are open in theinner edge62 of theliner38. Theradial grooves66 intersect thespiral groove64 at several points as shown.

In the third embodiment shown in FIGS. 8 and 9, theliner38 has asingle groove68 which is elliptical, centered on the axis A1 of theliner38. The major axis A2 of the ellipse is shorter than the outer diameter of the liner.Radial grooves70 provide communication between theelliptical groove68 and theinternal edge62 of theliner38.

As can be seen most particularly in FIGS. 7 and 9, the depth of thevarious grooves54,56,58,60,64,66,68,70 is substantially equal to one half of the axial thickness of theliner38.

These various embodiments of the invention show that the grooves may take a number of very different forms, so that the invention is not limited to those described above by way of example. Thus for example, it is possible to form radial grooves which are substantially developments of a circle.

In general terms, the various geometries proposed for the network of grooves in thefriction liner38 enable the torque that can be transmitted by the bridgingclutch30 to be increased, while at the same time limiting heating of theliner38 and heating of the oil when the clutch30 is in a slipping mode.

In addition, the invention is not limited to the use of a single friction liner. Theliner38 can, in this connection, cooperate with a further liner carried by the reaction surface.

Claims (6)

What is claimed is:

1. A friction liner for a torque converter bridging clutch having a reaction surface, the liner being annular and comprising:

a radially outer edge,

a radially inner edge, and

an annular friction surface adapted for engagement with said reaction surface, the friction surface defining a network of grooves therein for circulation of a liquid between the liner and said reaction surface,

wherein communication between the network of grooves and the outer edge of the liner is absent, and wherein the network of grooves comprises a spiral groove and a set of radial grooves open at the inner edge of the liner and intersecting the spiral groove at a plurality of points.

2. A friction liner according to claim1, wherein said grooves have a depth substantially equal to one half of the axial thickness of the liner.

3. A friction liner according to claim1, made of a composite material including carbon.

4. A bridging clutch for a torque converter having a casing, the bridging clutch comprising:

a movable annular clutch plate for engagement with a reaction surface of the casing; and

a friction liner according to claim1 affixed to the clutch plate.

5. A friction liner according to claim1, wherein the grooves have a U-shaped cross section.

6. A friction liner according to claim1, made of a composite material comprising a resin in which reinforcing elements are embedded.

Images